1. Field of the Invention
The present invention generally relates to an active damping apparatus capable of exhibiting dynamic vibration damping action by means of actively controlling pressure fluctuations in a pressure receiving chamber having non-compressible fluid sealed therein, and in particular relates to a fluid-filled active damping apparatus wherein a portion of the wall of the pressure receiving chamber is formed by a displaceable oscillation plate, and pressure in the pressure receiving chamber is controlled on the basis of excited displacement of the oscillation plate by means of an actuator.
2. Description of the Related Art
Fluid-filled active damping apparatus are known as one type of vibration damping connector or vibration damping support interposed between components targeted for damping, such as an automotive engine mount or body mount, to provide vibration damping linkage of components. A damping apparatus of this kind includes: a first mounting member attachable to one of the two components being linked in the vibration damping fashion; a second mounting member attachable to the other of the two components; a rubber elastic body elastically connecting the first and second mounting members; a pressure receiving chamber whose wall portion is partially constituted by the rubber elastic body, and subjected to input of vibration; an equilibrium chamber whose wall portion is partially constituted by a flexible diaphragm, and having a variable volume. These pressure receiving chamber and equilibrium chamber have a non-compressible fluid sealed therein, and held in fluid communication to each other through an orifice passage. In the damping apparatus of this design, when vibration is applied to the pressure receiving chamber, on the basis of the pressure difference created between the pressure receiving chamber and the equilibrium chamber, fluid is forced to flow through the orifice passage, whereby passive vibration damping effect is exhibited on the basis of resonance action or other flow action of the fluid.
A vibration damping apparatus of this kind that utilizes only passive vibration damping action, have a difficulty in providing sufficient vibration damping action in the event that the frequency or other characteristics of vibration targeted for damping should change, or that higher vibration damping action is required.
In recent years, there has been developed and tested dynamic vibration damping apparatus of fluid-filled that utilize an electromagnetic or pneumatic actuator to dynamically control the pressure of the pressure receiving chamber in a cycle corresponding to the frequency of the vibration targeted for damping, in order to actively reduce vibration. In such a dynamic vibration damping apparatus, as taught in JP-A-2002-188677, for example, another portion of the wall of this pressure receiving chamber is constituted by an oscillation plate. The oscillation plate is elastically supported and capable of displacement on the second mounting member etc. via a rubber elastic body, with pressure of the pressure receiving chamber being controlled on the basis of excited deformation of the plate by the actuator. With this arrangement, for example, in response to relatively low-frequency vibration such as engine shake etc., it is possible to obtain passive vibration damping effect on the basis of resonance action or other flow action of fluid through the orifice passage (orifice effect). In addition, in response to relatively high-frequency vibration such as idling vibration or driving rumble or booming noises, it is possible to obtain dynamic vibration damping effect on the basis of pressure control of the pressure receiving chamber by means of displacement of the oscillation plate.
However, in a fluid-filled dynamic vibration damping apparatus, since deformation of the oscillation plate is permitted on the basis of elastic deformation of a supporting rubber elastic body, during input of vibration in the low frequency range which requires the orifice effect, the pressure fluctuations of the pressure receiving chamber are absorbed by means of elastic deformation of the supporting rubber elastic body and associated displacement of the oscillation plate. As a result, it is difficult to produce a sufficient pressure difference between the pressure receiving chamber and the equilibrium chamber, the flow of fluid through the orifice passage drops, and there is a risk that passive vibration damping action on the basis of resonance action etc. of the fluid will not be advantageously obtained.
To address this problem, it has been contemplated to cause static drive force to act on the oscillation plate and the supporting rubber elastic body in order to maintain a constrained state, as taught in JP-A-2002-295571, for example. However, in a dynamic vibration damping apparatus, if constriction force at a level adequate to constrain displacement is exerted on the oscillation plate and the fluid-filled dynamic vibration damping apparatus, appreciable stress and deformation are produced in the supporting rubber elastic body, and problems of permanent set in fatigue and/or durability thereof tend to occur. An additional problem is that where both passive vibration damping effect by the orifice passage and dynamic vibration damping effect by displacement of the oscillation plate are required at the same time, it may not be possible to handle the situation appropriately.
In fluid-filled dynamic vibration damping apparatus of the conventional designs described hereinabove, in order to achieve dynamic vibration damping effect, it is necessary to subject the pressure receiving chamber to the action of pressure fluctuations that, with as high a degree of precision as possible, correspond to the frequency and waveform of the vibration targeted for damping.
However, the fact is that in actual practice it is difficult to make pressure fluctuations exerted on the pressure receiving chamber by means of exciting actuation of the oscillation plate correspond with high precision to vibration targeted for damping. There are several reasons for this. For example, typically the actuating force of the actuator acts on the oscillation plate in only one direction, with return motion in the opposite direction produced by the elastic behavior of the supporting rubber elastic body, so that one cause is a difference in actuating force between outbound and return. Another cause is high order components of elastic deformation of the supporting rubber elastic body per se which elastically supports the oscillation plate. In constructions in which the oscillation plate undergoes excited displacement by a pneumatic actuator, yet another cause is that during excited actuation by means of switching air pressure, pressure pulsations are produced on the air pressure transmission path. In constructions that employ an electromagnetic actuator that uses electromagnetic or magnetic force, another cause is that since the relative positions of the movable element and the stationary element change in association with displacement of the movable element, the generated force changes as well. Additionally, where generated actuating force is controlled by means of an electrical signal, another cause is high frequency components produced in the actuating force, due to noise of various kinds in the electrical signal.
To cope with these problems, there has been proposed, for example in JP-A-2004-52872, a construction in which a partition member is provided to the pressure receiving chamber, dividing the pressure receiving chamber into a primary fluid chamber whose wall is partially constituted by a rubber elastic body, and an auxiliary fluid chamber whose wall is partially constituted by the oscillation plate, with a filter orifice provided between the primary fluid chamber and the auxiliary fluid chamber. This is, by tuning the filter orifice to a lower frequency range than the high order components causing the problem, pressure fluctuations produced in the auxiliary fluid chamber are exerted on the primary fluid chamber, in a condition in which high order components have been eliminated.
However, with the dynamic vibration damping apparatus taught in JP-A-2004-52872, in the event that large-amplitude vibration is input to the pressure receiving chamber, pressure fluctuations of the primary fluid chamber are transmitted to the auxiliary fluid chamber through the filter orifice regardless of whether the filter orifice has been tuned. As a result, the pressure of the pressure receiving chamber (the primary fluid chamber and the auxiliary fluid chamber) escapes due to deformation of the oscillation plate constituting the wall of the auxiliary fluid chamber and of the supporting rubber elastic body, making it difficult to ensure an adequate pressure difference between the pressure receiving chamber and the equilibrium chamber. Thus, the aforementioned problem of not being able to achieve the desired passive vibration damping action due to the difficulty of ensuring adequate fluid flow through the orifice passage remains unresolved.